Size alone tells youEach NEF, CR3 and ARW contains an embedded JPEG for preview purposes, which gives the camera's screen something to show. An ordinary utility extracts that JPEG, marks the RAW as recovered, then moves on to the next file. This explains why a 50MB RAW frame comes back at around 5MB.
Large files seldom sit in one runA continuous block of free space long enough for a large file is relatively rare on a memory card. When a basic carver reaches the first gap, it stops, costing you a corner of a JPEG and the whole of a RAW image or video clip. The order of these runs is recorded within the file format itself, and knowing how to read it is what makes the difference.
Each RAW format gives way in its own mannerTIFF is the underlying format used for CR2 files, which is why CR2 files tend to survive damage better than many other formats. CR3 files use a newer container built on other principles. Damage to NEF files generally appears as bands of green and purple across the image. ORF, RAF, RW2, ARW and DNG each need handling on their own terms, and no single off-the-shelf utility covers them all.
What a deletion really removesDeleting a file on FAT or exFAT releases the cluster chain the file used, while a format releases all of them at once. Your card is never wiped, which is why recovery works so well, and also why your very next shot may be written straight over an image you want.